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Groups > linux.kernel > #1240787
| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() |
| Date | 2015-10-06 19:40 +0200 |
| Message-ID | <qgEnx-4wt-27@gated-at.bofh.it> (permalink) |
| References | <qgD85-2O1-3@gated-at.bofh.it> <qgD85-2O1-5@gated-at.bofh.it> <qgDhM-2Zi-17@gated-at.bofh.it> <qgE4a-49R-29@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tue, Oct 06, 2015 at 10:18:39AM -0700, Josh Triplett wrote:
> On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote:
> > Currently, __srcu_read_lock() cannot be invoked from restricted
> > environments because it contains calls to preempt_disable() and
> > preempt_enable(), both of which can invoke lockdep, which is a bad
> > idea in some restricted execution modes. This commit therefore moves
> > the preempt_disable() and preempt_enable() from __srcu_read_lock()
> > to srcu_read_lock(). It also inserts the preempt_disable() and
> > preempt_enable() around the call to __srcu_read_lock() in do_exit().
>
> What restricted environments do you intend to invoke
> __srcu_read_lock from?
>
> This change seems fine, but I don't see any change in this patch series
> that needs this, hence my curiosity.
Someone asked me for it, and now I cannot find it. :-(
Something to the effect of when running unmapped during exception entry
or something like that. I guess one way to find out would be to remove
the commit and see who complained, but on the other hand, it arguably
makes more sense to have only the bare mechanism is __srcu_read_lock()
and put the environmental protection into srcu_read_lock().
Thanx, Paul
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> > include/linux/srcu.h | 5 ++++-
> > kernel/exit.c | 2 ++
> > kernel/rcu/srcu.c | 2 --
> > 3 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> > index bdeb4567b71e..f5f80c5643ac 100644
> > --- a/include/linux/srcu.h
> > +++ b/include/linux/srcu.h
> > @@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
> > */
> > static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
> > {
> > - int retval = __srcu_read_lock(sp);
> > + int retval;
> >
> > + preempt_disable();
> > + retval = __srcu_read_lock(sp);
> > + preempt_enable();
> > rcu_lock_acquire(&(sp)->dep_map);
> > return retval;
> > }
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index ea95ee1b5ef7..0e93b63bbc59 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -761,7 +761,9 @@ void do_exit(long code)
> > */
> > flush_ptrace_hw_breakpoint(tsk);
> >
> > + TASKS_RCU(preempt_disable());
> > TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
> > + TASKS_RCU(preempt_enable());
> > exit_notify(tsk, group_dead);
> > proc_exit_connector(tsk);
> > #ifdef CONFIG_NUMA
> > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
> > index 9e6122540d28..a63a1ea5a41b 100644
> > --- a/kernel/rcu/srcu.c
> > +++ b/kernel/rcu/srcu.c
> > @@ -298,11 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp)
> > int idx;
> >
> > idx = READ_ONCE(sp->completed) & 0x1;
> > - preempt_disable();
> > __this_cpu_inc(sp->per_cpu_ref->c[idx]);
> > smp_mb(); /* B */ /* Avoid leaking the critical section. */
> > __this_cpu_inc(sp->per_cpu_ref->seq[idx]);
> > - preempt_enable();
> > return idx;
> > }
> > EXPORT_SYMBOL_GPL(__srcu_read_lock);
> > --
> > 2.5.2
> >
>
--
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[PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.4 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
Re: [Kernel networking modules.] OSI levels 2 & 3, Assistance - If anyone knows anyone in the US. North West region "John D Allen, Leveridge Systems INC" <john.allen@leveridgesystems.com> - 2015-10-06 18:30 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Josh Triplett <josh@joshtriplett.org> - 2015-10-06 18:50 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:20 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:50 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:50 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Peter Zijlstra <peterz@infradead.org> - 2015-10-06 22:10 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 22:20 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Peter Zijlstra <peterz@infradead.org> - 2015-10-06 23:00 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 23:10 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers Peter Zijlstra <peterz@infradead.org> - 2015-10-07 09:30 +0200
Re: [PATCH tip/core/rcu 04/13] rcu: Don't disable preemption for Tiny and Tree RCU readers "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:20 +0200
[PATCH tip/core/rcu 03/13] rcu: Use call_rcu_func_t to replace explicit type equivalents "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 01/13] sched: Export sched_setscheduler_nocheck "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 09/13] rcu: Correct comment for values of ->gp_state field "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 02/13] rcu: Use rcu_callback_t in call_rcu*() and friends "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 12/13] rcu: Remove deprecated rcu_lockdep_assert() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
[PATCH tip/core/rcu 06/13] rcu: Add online/offline info to stall warning message "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:20 +0200
Re: [PATCH tip/core/rcu 06/13] rcu: Add online/offline info to stall warning message Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:20 +0200
[PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:30 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:20 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:40 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:50 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 20:10 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Peter Zijlstra <peterz@infradead.org> - 2015-10-06 22:10 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 22:20 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Peter Zijlstra <peterz@infradead.org> - 2015-10-06 22:40 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 23:10 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Peter Zijlstra <peterz@infradead.org> - 2015-10-07 09:30 +0200
Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-07 16:20 +0200
[PATCH tip/core/rcu 05/13] rcu: Eliminate panic when silly boot-time fanout specified "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:30 +0200
[PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 18:30 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:30 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:40 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:40 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() Peter Zijlstra <peterz@infradead.org> - 2015-10-06 22:30 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 23:10 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() Peter Zijlstra <peterz@infradead.org> - 2015-10-07 09:30 +0200
Re: [PATCH tip/core/rcu 10/13] rcu: Add rcu_pointer_handoff() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-07 16:30 +0200
Re: [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.4 Josh Triplett <josh@joshtriplett.org> - 2015-10-06 19:30 +0200
Re: [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.4 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-06 19:40 +0200
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